Which of the following skills is emphasized in seamanship?

Seamanship primarily focuses on the skills required for the safe and effective operation of a vessel, which includes managing sailing and navigation. This encompasses a broad range of practical skills such as understanding how to handle sails, operate a motor, navigate using charts and compass, and ensure the vessel's safety at sea. The knowledge of navigation is crucial for determining a ship's position, plotting courses, and understanding maritime rules and regulations, which are key components of seamanship.

While the other options involve important skills in their respective areas—military strategy, survival techniques, and communication—they do not directly pertain to the core competencies required in working effectively on watercraft. Seamanship is specifically the art and science of operating a ship and understanding the principles of the maritime environment, making management of sailing and navigation the correct emphasis in this context.